Refining of glyceride oils



B. CLAYTON REFINING OF GLYCERIDE OILS Filed Sept. 18, 1950 ,lla

INVENT OR ATTORNEYS riff/115151. .1J

/ l l f l l f l l f l l 5 l,

saAP PuR/Ffa: 5700/( Patente-d June 9, 1953 REFINING F GLYCERIDE OILS Benjamin Clayton, Pasadena, Calif.

Application September 18, 1950, Serial No. 185,434

Claims.

` This invention relates to the refining of glyceride oils, and more particularly, to -a simplified continuous alkali rening process in which re ining losses are minimized while at the same 4time a high quality oil is produced.

The original commercial continuous process of alkali refining glyceride oils, which process is still extensively employed, involves the continuous mixing of an aqueous solution of caustic soda having a concentration between lapproximately and 20 B. with the oil in an amount sufcient lto neutralize the acidity of the oil and also provide a substantial excess. The mixture is continuously centrifugally separated into oil and soapstock at an elevated temperature, usually between 120? and 160 F., the elevated temperature being produced by heating the materials in Astream flow either before mixing or after mixing.

While such process produces a high quality oil and materially reduces rening losses over the earlier developed batch process of alkali refining glyceride oils, a substantial loss of neutral oil results both from saponi'cation of neutral oil by the excess caustic soda and from entrainment of a considerable amount of neutral oil in the soaps-tock separated from the oil.

An improved process known as the soda ash process is also in large scale commercial operation and involves the addition of an aqueous solution of soda ash to the oil in substantial excess. Such a mixture is not easily separable into neutral oil and soapstock, since carbon dioxide is evolved and interferes with separation of the soapstock from the oil. In lorder to overcome this diiiiculty, the mixture is introduced into a flash chamber while at an elevated temperature and subjected to a vacuum therein. The carbon dioxide and the major portion of the water are thereby removed from the mixture. The dehydrated mixture is thereafter rehydrated with additional soda ash solution and continuously separated in ya centrifugal separator, With light colored oils, for example, corn oil or peanut oil, a satisfactory rened oil may be produced and the refining losses are very low. That is to say, the soda ash will not saponify the neutral oil so that refining losses due to saponilcation of neutral oil are entirely eliminated and the dehydration and rehydration steps condition the oil for very effective centrifugal separation such that losses of oil by entrainment of the oil in the soapstock are also substantially eliminated. For dark colored oils, such as cottonseed oil and in some cases even light colored oils, it is desirable to re-rene or caustic Wash the oil employing a small amount of relatively concentrated caustic soda solution. Losses in the re-rening step are `also very small and a high quality neutral oil is produced with a minimum of rening losses.

The present process departs from either of the prior processes above discussed by first employing a relatively concentrated aqueous solution of caustic soda in an amount which is not substantially greater than that required to neutralize the acidity of the oil and which will not saponify any appreciable amount of neutral oil. That is to say, the amount of caustic soda should not be used in substantial excess but in some cases may be somewhat less than that required to neutralize the acidity of the oil. In any case, the acidity of the oil mixture after the addition of caustic soda is not suicient to cause the liberation of carbon dioxide upon addition of soda ash solution. The caustic soda solution 4preferentially combines with the fattyv acids and other acidity Y of the oil before it attacks neutral oil. Since no substantial excess is employed and the strong' caustic solutions attack neutral oil to a lesser extent than more dilute caustic solutions, substantially n-o saponication of the neutral oil takes place during the caustic soda treatment. Since the caustic soda solution is quite concentrated, the resulting mixture is loW in Water content and may be considered to be a partially dehydrated mixture. Such a mixture cannot be eiciently separated in a continu-ous centrifugal separator as the foots or soapstock are thick and viscous and will entrain a substantial amount of neutral oil. Also the soap does not separate cleanly from the oil. However, it has been found that by adding a substantial amount of sod-a ash solution to such a mixture before introduction into the centrifugal separator or during separation in the centrifugal separa-tor, va relatively liquid soapstock in which very little neutral oil is entrained can be readily separated from the neutral oil. As in the soda ash process discussed above, a high quality refined oil may be produced from light colored oils with minimum refining losses. However, for dark colored oils a refrelning step involving the addition .of a relatively concentrated caustic soda solution followed by continuous centrifugal separation is desirable in order to reduce the color of the oil. Also in many cases the re-reining step may be advantageously employed even for light colored oils to remove residual impurities. As in the commercial soda ash process the losses in the re-rening step are also very low. The improved process of the present invention therefore produces a high quality oil with a minimum of rening losses while at the same time eliminating the dehydration step of the commercial soda ash process along with the extensive apparatus and heat losses associated therewith.

It is therefore an object of the present invention to provide an improved process for alkali refining glyceride oils in which rening losses are minimized.

Another object of the invention is to provide a process of alkali rening glyceride oils in which caustic soda is employed as the neutralizing agent but losses due to saponiication of neutral oil and entrainment of neutral oil in the soapstock separated from the oil are largely eliminated.

A further object of the invention is to provide an improved yprocess of alkali refining of glyceride oils in which a relatively concentrated caustic soda solution is employed as a neutralizing agent in an amount not substantially in excess of that required to neutralize the acidity of the oil and a soda ash solution is thereafter employed to render the resulting mixture separable.

Other objects and advantages of the invention Will appear in the oliowing detailed description thereof in which reference is made to suitable apparatus for carrying out the process, which apparatus is shown in the attached drawing.

Referring to the drawing, the glyceride oil to be refined may be supplied from the tank I il. Caustic soda solution for neutralizing the oil may be supplied from the tank i I and soda ash solution may be supplied from the tank i2. The oil may be pumped from the tank Iii by means of a pump I3 and delivered through a heater l to the mixer I6. In a similar manner the caustic soda solution may be pumped from the tank `I I by means of the pump I? and passed through the heater IB to the mixer i5. The oil and caustic soda solution are thoroughly and rapidly mixed in the mixer Ia, which mixer may be of any known or suitable type and the resulting mixture under pressure from the pumps I3 and Il may be delivered through another heater i9 to a second mixer 2 I. Soda ash solution may be pumped from the tank i2 by means of the pump 22 and delivered passed through another heater 26 and delivered into a continuous centrifugal separator 2l.

The pumps I3, il and 22 may be proportioning pumps forming part or" a proportioning apparatus. That is to say, the three pumps may be driven by a variable speed motor 28 and speed change devices 29 and 3i may be interposed between the motor 28 and the pumps Il and 22, respectively, although any other suitable type of proportioning apparatus may be employed. IThe various heaters I4, I8, I, 23 and 25 are shown as including coils 32 through which the material to be heated is passed, the coils being positioned in the casings 33 through which any desired heating medium, such as steam, may be passed by means of the pipe connections 34 and 36. Any other suitable type of heating apparatus may, however, be employed. Although the devices including the coils 32 and casings 33 have been referred to as heaters it will be apparent that they are in fact heat exchange devices and can be employed for cooling the material being passed therethrough, if desired, by passing a cooling medium through the casings 'e3 by means of the pipe connections 34 and 3S. Thus the various materials may be brought to the desired temperatures in the heat exchangers and if no temperature change is required in a particular case, the heat exchanger may be by-passed or in the case of a mixture, a heat exchanger maybe employed to provide greater time of contact between the constituents of the mixture with or without changing the temperature of the mixture.

If in treating a particular oil, it is found desirable to minimize the time or" contact vbetween the oil and the caustic soda solution, the heaters itl and i8 may be employed to bring the oil and caustic soda solution to a desired temperature and the heater i9 may be by-passed by means of the conduits 3i and 3d. Similarly, if it is desired to minimize the time of contact after the soda ash solution has been added, the heater 25 may be bypassed by means ci the conduit te. In fact, in some instances it is desirable to add the soda ash solution just before the mixture or" oil and caustic soda enters the centrifugal separator 27, in which case the mixer 2i and heater 26 may be by-passed by the soda ash solutionby employing the conduit Iii. In the latter case, the'mixture of oil and caustic soda may be passed through the heater I9 and mixer 2i or the heater I9 may be 4by-passed. Infact, the mixer 2 I may likewise be by-passed by employing the conduit d2. That is to say, the mixture of caustic soda and oil can be either sent directly to the centrifugal separator through the conduits Si, L32 and Se or may be sent lthrough any desired combination of the heaters I9 and 26 and the mixer 2i. In some cases, it may be desirable to add the soda ash solution as a flush within the centrifugal separator itself in which case a centrifugal separator of the type disclosed in Clayton Patent No. 2,412,251 may be employed.

In the centrifugal separator 2'! a separation is made between the neutral oil and soapstock, the soapstock being discharged as the heavier eiuent through the spout #t3 into a tank Gli. The neutral oil is discharged as the lighter eiuent through the spout it into a tank il?. Where light colored oils, such as corn oil or peanut oil are being refined, the oil delivered into the tank l?? may constitute the nal product and may be discharged from the process through the conduit although it is many times desirable to remove residual impurities from even light colored oils by the rereiining step referred to above, For dark colored oils, for example cottonseed oily it is usually desirable to subject the reiined oil to such a re-rening treatment involving the addition to the oil of a small amount of caustic soda solution. In such cases the oil from the tank l? may be pumped from such tank by means of the pump 49, passed through a heater 5i and delivered to a mixer 52. Caustic soda solution from a tank 53 may be delivered by the pump 5d through the heater 56 to the mixer 52. The mixer 52 may be any known or suitable type and may be similar to the mixers i6 and 2l. The resultinCT mixture may then be passed through another heater 57 and delivered into a centrifugal separator 5%.

It is usually desirable to add a diluting agent to the mixture just prior to centrifugal separation and this may be accomplished by withdrawing a diluting agent, such as water, from the tankV 59 by means of a pump 6I, passing the same through a heater S2 and introducing the same into the conduit 63 which supplies the mixture of oil and caustic soda solution to the centrifugal separator 58. The heaters 5i, 55, 5'! and 5.2, may be of any suitable type and may be similar to the heaters it, I8', etc. Again, the. centrifugal separator 58 maybe of the type shown in Clayton Patent aaai-eos No. 2,412,251 in which case the diluting agent may be delivered directly into the centrifugal separator as a flush. In the centrifugal separator 58 the purified oil is separated from the soapstock and discharged as a lighter effluent through the spout 64 into a tank 65 from which it may be withdrawn from the process and a small amount of soapstock containing the diluting agent, if employed, is discharged as a heavier effluent through a spout 6l into a tank 68.

In carrying out the process a relatively strong caustic soda solution is initially admixed with the oil, i. e., the caustic soda solution delivered to the mixer i6 from the tank Il will have a concentration between approximately 25 and 50 B., concentrations in the range of from 25 to 40 B. being preferred. Sufcient caustic soda solution is preferably employed to neutralize the acidity of the oil. That is to say, no substantial excess' of caustic soda solution is used. The amount of caustic soda solution required to neutralize the acidity lof the oil Vmay be determined according to the American Oil Chemists Society Official Methods. The oil and caustic soda are preferably contacted with each other at a relatively low Itemperature, for example, a temperaturebetween 70 and 110 F., the lowertemperatures in this range being preferred. rI'hat is t0 say, the heaters lll and I8 may be employed to either raise or lower the temp-erature of the oil and caustic soda solution to bring 4their temperature within the desired range. If no adjustment of temperature of the oil or caustic soda solution is required, prior to mixing, the heaters l5 and I8 may be by-passed by conduits (not shown). In general, it is not usually desirable to increase the temperature of the mixture of caustic soda and oil much above 110 F., prior to the addition of the soda ash solution.

The temperature of separation after addition of the soda ash solution will usually range, however, between 100 and 160 F., and may be as high as 200 F., and the heater I9 may be employed to raise the temperature of the caustic soda and oil mixture up to not more than 110 Ff. and the heater 26 may be employed to raise the temperature Iof the resulting mixture of soda ash, caustic soda and oil to the desired separation temperature.

It will .be appreciated that the exact mixing and heating sequence employed may be varied and it is desirable to provide for such variations since the various glyceride oils vary considerably in properties and it has been found that certain oils -respond better to heating before admixture with for example in the Amixer 2 I, or-require a longer time of contact between the soda ash solution andthe previously made caustic soda and oil mixture, in which case the heater 26 may be employed for such purpose.

In general, the caustic soda should be rst thoroughly admixed with the oil at a temperature between approximately 70 and 110 F., the temperature of this mixture should not be increased materially above 110 F., and a soda ash solution should thereafter be admixed with the oil and separation should take place at a temperature between approximately 100 and 160 F. In many cases, a relatively high temperature of separation may be obtained by delivering the mixture of oil and caustic soda to the centrifuge at a relatively low `temperature and supplying to the centrifuge a relatively hot flush of soda ash solution.

The soda ash-solution will usually have a concentration between 10 and 20 B. and will be employed in anv amount ranging between approximately 1 and 5% of the solution by weight based on the amount of oil. In general, the amount and concentration of the soda ash solution should be such as to increase the moisture content of ythe soapstock discharged from the centrifugal separator 2l up to 25 to 50% by weight of the soapstock.

As stated above, light colored oils delivered into the tank 4'! from the centrifugal separator 2l may be discharged from the process as refined oil but dark colored-oils, in general, do not have their lcolor sufficiently removed in the process just described. Furthermore, even light colored oils are usually benefited by re-rening with caustic soda in accordance with the disclosure of Clayton Patent No. 2,412,251. Thus in accordance with the disclosure of such patent, the oil from the tank 41 may be admixed with a caustic soda lsolution in the mixer 52 and sent to the centrifugal separator 58. A diluting agent, for example water, or a dilute solution of soda ash may be injected into the mixture of oil and caustic soda solution just prior to introduction of said mixture into the centrifugal separator 58, or even within the centrifugal separator itself as disclosed in such patent.

'Ihe concentration of the caustic soda solution from the tank 53 will, in general, range between about 20 and 50 B. and the amount of such solution will usually range between approximately 0.5% and 4%, the quantity most generally used being in the neighborhood of 2% based onY the Weight of the oil. The temperature of mixing is preferably between '70 and 100 F.faithough for removing certain types of impurities, this temperature may be as high as 130 to 140 F., the heaters 5I and 56 being employed for adjusting the temperature of the materials being mixed in the mixer 52. The temperature of separation will usually range between 120 and 180 F., and preferably between 120 and 160 F., although with some oils this temperature may be as low as 100 Y caustic soda solution employed. In general, it

' found advantageous.

has beenfound desirable to reduce the concentration of the excesscaustic soda solution in the centrifugal separator to at least 8 B. although in some instances higher concentrations up to 10 or 12 B. have been found operable and in other cases, concentrations as low as 4 B. have been The heavier effluent discharged through the spout `6l contains a small amount of soap, and in anyl event, the amount of water or otherdiluting agent employed in the centrifugal separator should be suicient to cause the soap to cleanly separate from the oil in solution or dispersion in `the aqueous phase. The temperature of the diluting agent should, in general, be at least as high as the temperature of the oiland caustic soda mixture entering the centrifugal separator and may be somewhat higher.

It is usually desirable to subject the oil discharged from the re-rening step, or if no rerefining step is employed, the oil from the initial refining step, toa water washing treatment involving mixing of water with the oil in an amount between approximately to A20% of the oil by weight and .centrifugally vseparating the water from the oil.

The present process is thus an limprovement over the commercial caustic soda processes -in that it materially reduces the rening losses including losses Idue to saponiiication of neutral oil and entrainment of neutral oil in the soapstock and is an improvement over the sodaaash process in that it eliminates the dehydration-step employed therein while at the ysame time resulting in reiining losses as low or lower than the soda ash process. A

The process'of the present invention is applicable to substantially all types of glyceride oils including animal, vegetable and marine oils as it is sumciently Flexible to produce-a high-quality oil with low losses when employed to refine nearly any type of glyceride oils likely to beencountered. The process produces particularly good results with low vfree fatty acid oils lor oils containing a low ratio of free fatty acids to gums but may be employed to produce excellent results even vwith high free fatty 4acid oils or previously degummed oils. The present` process avoids vthe employment ofthe large amounts lof soda ash found necessary when refining high s free vfatty Yacid oils and also avoids the evaporation of large amounts of water in a dehydration step.

I claim:

1. The process of alkali reiining a iglyceride oil, which comprises, mixing a concentrated aqueous solution of caustic soda with said oil, said solution of caustic soda having a concentration between approximately 25 and 50 B.

and being added in an amount suiiicient to neutralizethe acidity Vof said oil without providing any substantial excess of said caustic soda, thereafter a-dmixing an aqueous solution of soda ash with said oil and continuously centrifugally separating the resulting aqueous soapstock from said oil, the amount and concentration of said soda ash solution being'sufcient Vto cause said scapstocl; to separate cleanly from said oil.

2. The process of alkali refining glyceride oils, which comprises, admixing with said oil a caustic soda solution having a concentration between approximately 25 and 50 B. in suiiicientamount to substantially completely Vneutralize the acidity of said oil without providing any substantial excess of caustic soda to produce a neutralized mixture having a relatively low water content, thereafter admixing with said mixture a soda ash solution having a concentration between approximately and 20 B. in an amount between approximately l% and 5% of solution based on the oil and continuously centrifugally separating soapstock from said oil.

3. The process of alkali refining a Vglyceride oil, which comprises, continuously mixing a stream of said oil and a stream of caustic soda solution y ,f5 Vand 50 B., :the-,amount of ysaid solution be.- ing sufficient to neutralize the acidity `of ,said oil without providinga substantial excess .of .caustic soda, thereafter admixing arsolution of soda ,ash with said oil and continuously centrifugally separating soapstock from said toil, said soda ash solution having a concentration between approximately 10 and 20 B. and being sufficient in amount to produce alsoapstock having between approximately and 50% water content by f weight. Y

4. The process of alkali refining `a glyceride oil, which comprises, mixing a concentrated aqueous solution of caustic soda-with said oil, said ,solution of caustic soda having ,a concentration between approximately25 `and 50 B. and 'being .added .in an amount sufficient to neutralize the .acidity of said cil without providing any substantial excess of said caustic soda, maintaining the temperature of said oil and solution of caustic soda at a temperature not higher than approximately 110 F., thereafter admixingan aqueous solution of soda ash with said oi1,and continuously centrifugallvk separating the resulting aqueous soapstock from said oil at a temperature between approximately and 160 F.1said solution of soda ash having a concentration `between approximately 10 and 20 B. and being added in an amount sufficient to cause-saidsoapstock to separate cleanly from said oil.

5. The process of alkali refining a glyceride oil, which comprises, mixing a concentrated aqueous solution of vcaustic soda withsaid oil, said solution of caustic soda having a concentration between approximately 25 and .50 B. and being added in an amount suiiicient to neutralize 'the acidity of said oil without providing any substantialexcess of said causticsoda, maintaining the temperature of said oil and solution of caustic soda at a temperature not higher than approximately F., thereafter admiXng .an aqueous solution of soda ash with said oil .and continuously centrifugally separating ,the result- Ving aqueous soapstock from said oil at a rtemperature between approximately 100 and .160 F., said solution .of soda ash having a concentration between Vapproximately 10 and 20 B. and being added in an amount sufficient to c ause said-soapstock to separate cleanly from said oil, and thereafter mixing said oil with a solution of caustic soda having la'concentration,between approximately 20 `and 50 B. and in an amount between approximately 40.5% and 4% of the weight of said oil, and continuously centrifugally separating an additional amount of soapstock from said oil at a temperature between approximately yand 180 F. f

v BENJAMIN CLAYTON.

References Cited in the le of `this patent vUNITED STATES PATENTS Clayton July 15, ,1941 

5. THE PROCESS OF ALKALI REFINING A GLYCERIDE OIL, WHICH COMPRISES, MIXING A CONCENTRATED AQUEOUS SOLUTION OF CAUSTIC SODA WITH SAID OIL, SAID SOLUTION OF CAUSTIC SODA HAVING A CONCENTRATION BETWEEN APPROXIMATELY 25* AND 50* BE. AND BEING ADDED IN AN AMOUNT SUFFICIENT TO NEUTRALIZE THE ACIDITY OF SAID OIL WITHOUT PROVIDING ANY SUBSTANTIAL EXCESS OF SAID CAUSTIC SODA, MAINTAINING THE TEMPERATURE OF SAID OIL AND SOLUTION OF CAUSTIC SODA AT A TEMPERATURE NOT HIGHER THAN APPROXIMATELY 110* F., THEREAFTER ADMIXING AN AQUEOUS SOLUTION OF SODA ASH WITH SAID OIL AND CONTINUOUSLY CENTRIFUGALLY SEPARATING THE RESULTING AQUEOUS SOAPSTOCK FROM SAID OIL AT A TEMPERATURE BETWEEN APPROXIMATELY 100* AND 160* F., SAID SOLUTION OF SODA ASH HAVING A CONCENTRATION BETWEEN APPROXIMATELY 10* AND 20* BE''. AND BEING ADDED IN AN AMOUNT SUFFICIENT TO CAUSE SAID SOAPSTOCK TO SEPARATE CLEANLY FROM SAID OIL, AND THEREAFTER MIXING SAID OIL WITH A SOLUTION OF CAUSTIC SODA HAVING A CONCENTRATION BETWEEN APPROXIMATELY 20* AND 50* BE''. AND IN AN AMOUNT BETWEEN APPROXIMATELY 0.5% AND 4% OF THE WEIGHT OF SAID OIL, AND CONTINUOUSLY CENTRIFUGALLY SEPARATING AN ADDITIONAL AMOUNT OF SOAPSTOCK FROM SAID OIL AT A TEMPERTURE BETWEEN APROXIMATELY 120* AND 180* F. 